The operation of modern integrated radio-frequency modules for mobile radio is no longer driven via control lines and, instead, they communicate with a control module (host) via a serial programming interface. The baseband processor is in this case in general the control module. A three-conductor system with a clock line, a data line and an enable line has become established for the interface between the control module and the integrated radio-frequency module. In the specialist literature, the enable line is frequently also referred to as the strobe line.
The so-called 3W Standard has been issued as a quasi standard for communication via an interface such as this. All of the communication is controlled and driven by the control module in accordance with the 3W Standard. When it is intended to transfer data from the control module to the integrated radio-frequency module, the control module activates the enable line, that is to say it sets the enable line to a specific, predetermined value. The control module then emits a clock on the clock line and the data bits in serial form in synchronism with this on the data line. As soon as the enable line is reset again, the output of the clock pulses and bits is stopped. The bits emitted during an active phase of the enable line form a so-called message. The number of bits emitted per message corresponds to the number of clock cycles during which the enable line is activated. The bits are, as far as possible, emitted such that the clock flank or rising edge always occurs in the centre of one bit period at the radio-frequency module. The radio-frequency module in each case receives the bits with this flank, provided that the enable line is activated.
A message contains both data bits and address bits. In the 3W Standard, the address bits are normally arranged at the end of a message. However, this does not represent any restriction, and the arrangement of the address bits within the message is not of importance.
The DigRF Standard has been developed because no data can be read on the data line from the radio-frequency module in the 3W Standard. An interface based on the DigRF Standard comprises a control part and a data part. The data interface is required only when the baseband processor cannot interchange the transmission data and received data in the normal analogue form with the integrated radio-frequency module. However, an interface for the control information is always required. In precisely the same way as in the 3W Standard, this interface in the DigRF Standard is in the form of a bus with three lines, that is to say a clock line, a data line and an enable line. The protocol which is used to transfer data via the interface in the DigRF Standard is not the same as the protocol in the 3W Standard.
The DigRF Standard defines a maximum protocol length of 32 bits, which is made up as follows. After the activation of the enable line by the control module, the control module first of all produces a read/write bit (R/W bit) on the data line, which indicates to the integrated radio-frequency module whether data is intended to be programmed into the integrated radio-frequency module or to be read from it. The control module then transmits a variable length address via the data line. In the case of a write access, this is then followed by the transmission of data bits. The number of data bits per message can in principle be chosen as required, provided that the number of data bits does not exceed the maximum value of 32−1−(number of address bits).
In the case of a read access, the enable line is reset by the control module once the address bits have been sent. However, the control module continues to emit clock pulses on the clock line and, starting with the third clock flank after the last address bit, waits for data from the integrated radio-frequency module.
The major differences between the 3W Standard and the DigRF Standard are shown in a summarized form in the following text. The 3W Standard allows only write accesses to the integrated radio-frequency module, while read accesses are also possible in the DigRF Standard. With the same number of data bits and address bits, a DigRF message comprises one bit more than the 3W Standard, owing to the read/write bit. The address bits are normally arranged at the end of a message in the 3W Standard, and at the start of a message in the DigRF Standard.
Since two different standards are now available for communication between the control module and the radio-frequency module, it is desirable to provide a capability which makes it possible for a radio-frequency module to interact not only with control modules operating in accordance with the 3W Standard but also with control modules operating in accordance with the DigRF Standard.